D9.7. A point charge of \( 4 \cos 10^{8} \pi t \mu \mathrm{C} \) is located at \( P_{+}(0,0,1.5) \), whereas \( -4 \cos 10^{8} \pi t \mu \mathrm{C} \) is at \( P_{-}(0,0,-1.5) \), both in free space. Find \( V \) at \( P(r=450 \), \( \theta, \phi=0) \) at \( t=15 \mathrm{~ns} \) for \( \theta=:(a) 0^{\circ} \); b \( 90^{\circ} \); (c) \( 45^{\circ} \).
Ans. \( 159.8 \mathrm{~V} ; 0 ; 143 \mathrm{~V} \)
